HP Deskjet 840 question

My parents got a new PC, which means loads of questions for me! They connected their printer to the PC (Win XP home SP2) and it works fine but every time they try to print the printer does not automatically turn itself on. It used to do it fine on their old pc, same OS, so am confused. Is there a simple fix for this?

Well, it may be in a standby mode I guess. But the power light (green) on the printer is not on, and when I send a document to print the power light then lluminates and the printer starts working without me touching it.